The first version of the Nikon Series E 50mm F1.8 lens was 135 grams, the one with a real narrow focusing grip. Bet it's quite sharp stopped down some. Not multicoated

The Hexanon 40mm F1.8 is 130 grams, guess it's not a 50mm, and you do have to correct the lateral color and only use it at F4-F5.6 or smaller if you're searching for that last bit of perfection.

Am looking at a last-model Pentax-M 50mm F2 lens, weighs 138 grams. Can't bring myself to say that this truly mediocre optic is as good as the Hexanon, but it might be better than the lenses you were talking about at some apertures.

The Canon EF 50mm F1.8 II lens weighs 130 grams, if you can figure some way to set the aperture on the thing. There are some fab 50mm F2.8-F4.5 enlarger lenses out there, weighing 65-90 grams, if you can figure out some way to focus them.

There's many superb (2 stops down) 50mm F2.8-F4.5 enlarging lenses out there, if you can put them together with a 110 gram helical focuser. The lenses tend to weigh between 65 and 100 grams. Most not multicoated except for Apo lenses, Fujinon EX, and last model EL-Nikkors.